Decompression sickness risk in rats by microbial removal of dissolved gas.

We present a method for reducing the risk of decompression sickness (DCS) in rats exposed to high pressures of H2. Suspensions of the human colonic microbe Methanobrevibacter smithii were introduced via a colonic cannula into the large intestines of the rats. While the rats breathed H2 in a hyperbaric chamber, the microbe metabolized some of the H2 diffusing into the intestine, converting H2 and CO2 to methane and water. Rate of release of methane from the rats, which was monitored by gas chromatography, varied with chamber H2 pressure. This rate was higher during decompression than during compression, suggesting that during decompression the microbe was metabolizing H2 stored in the rats' tissues. Rats treated with M. smithii had a 25% (5 of 20) incidence of DCS, which was significantly lower (P < 0.01) than the 56% (28 of 50) incidence of untreated controls, brought on by a standardized compression and decompression sequence. Thus using a microbe in the intestine to remove an estimated 5% of the body burden of H2 reduced DCS risk by more than one-half. This method of biochemical decompression may potentially facilitate human diving.